1. Field of the Invention
The present invention relates to a sliding nozzle device attached to the bottom of a molten steel container, such as a tundish, and more particularly to improvement of the fixing of both the refractory lower plate and the immersion nozzle of that sliding nozzle device.
2. Description of the Related Art
A sliding nozzle device (hereinafter referred to simply as a nozzle device) is attached to the bottom of a molten steel container, so as to control the amount of molten metal flowing out of the container. Generally, the nozzle device is made up of a fixing plate, a sliding plate, and an immersion nozzle. Alternatively, it is made up of an upper fixing plate, a sliding plate, a lower fixing plate, and an immersion nozzle.
FIG. 9 shows an example of a conventional nozzle device. (In FIG. 9, illustration of an upper fixing plate and a sliding plate is omitted for simplicity.) As is shown FIG. 9, the nozzle device comprises metallic case 1 having a tubular portion in the center thereof. Refractory plate 2 is fixed to metallic case 1. It has projection 2a formed in the center of the lower surface thereof. Projection 2a extends downward into the tubular portion of metallic case 1. Discharge hole 3 for discharging molten metal is formed in the center of refractory plate 2. Mortar 4 is interposed between metallic case 1 and refractory plate 2.
Immersion nozzle 5 is fixed to projection 2a of refractory plate 2. Mortar 4 is also interposed between metallic case 1 and projection 2a of refractory plate 2. Immersion nozzle 5 has stepped portion 5a, at which the outer diameter of immersion nozzle 5 is changed.
Four bolts 6 are welded to the bottom of metallic case 1. Annular push plate 7 formed of iron is provided such that the radially inside portion of its upper side is in contact with stepped portion 5a of immersion nozzle 5. Push plate 7 has four through-holes 8 formed at locations corresponding to four bolts 6, respectively, and bolts 6 extend via through-holes 8. Nuts 9 are threadably engaged with those portions of bolts 6 which are projected from push plate 7. When nuts 9 are tightened, the upper side of push plate 7 is pressed against stepped portion 5a of immersion nozzle 5, with the result that immersion nozzle 5 is firmly secured to refractory plate 2.
The conventional nozzle device mentioned above has the following problems:
(1) Refractory plate 2 is secured within case 1 by use only of mortar 4. Therefore, if immersion nozzle 5 is pressed against the bottom of refractory plate 2 too tightly, refractory plate 2 may be raised from metallic case 1, adversely affecting the parallelism between plate 2 and case 1. Since, therefore, immersion nozzle 5 cannot be tightly pressed against refractory plate 2, the sealing characteristic between plate 2 and nozzle 5 is not satisfactory.
(2) Immersion nozzle 5 is secured to refractory plate 2 by use of bolts 6, push plate 7 and nuts 8. With this construction, it may happen that bolts 6 will thermally expand during the use of the nozzle device. If bolts 6 thermally expand, the force exerted on immersion nozzle 5 by push plate 7 will be reduced, thus producing a gap between plate 2 and nozzle 5. As a result, the oxygen of the air flows into the gap, causing adverse effects, such as oxidation of nozzle 5. It should be also noted that immersion nozzle 5 cannot easily be secured to refractory plate 2 since bolts 6 have to be welded to metallic case 1 and since nozzle 5 has to be firmly pressed against plate 2 by use of push plate 7 and nuts 8.